U.S. patent application number 10/935412 was filed with the patent office on 2005-02-03 for abrasive free formulations for chemical mechanical polishing of copper and associated materials and method of using same.
Invention is credited to Baum, Thomas H., Bernhard, David, Jones, Michael, Ma, Ying, Verma, Deepak.
Application Number | 20050026437 10/935412 |
Document ID | / |
Family ID | 25467684 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050026437 |
Kind Code |
A1 |
Ma, Ying ; et al. |
February 3, 2005 |
Abrasive free formulations for chemical mechanical polishing of
copper and associated materials and method of using same
Abstract
An abrasive free formulation for chemical mechanical polishing
and method for using the formulation for polishing copper and
related materials. The abrasive free formulation has a high removal
rate on copper and a low removal rate on barrier material. The
abrasive free formulation comprises at least an oxidizing agent and
an activating agent.
Inventors: |
Ma, Ying; (Weatherford,
TX) ; Jones, Michael; (Phoenix, AZ) ; Baum,
Thomas H.; (New Fairfield, CT) ; Verma, Deepak;
(Scottsdale, AZ) ; Bernhard, David; (Newtown,
CT) |
Correspondence
Address: |
Oliver A. Zitzmann
ATMI, Inc.
7 Commerce Drive
Danbury
CT
06810
US
|
Family ID: |
25467684 |
Appl. No.: |
10/935412 |
Filed: |
September 7, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10935412 |
Sep 7, 2004 |
|
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09935805 |
Aug 23, 2001 |
|
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6800218 |
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Current U.S.
Class: |
438/689 ;
257/E21.304 |
Current CPC
Class: |
C09G 1/04 20130101; H01L
21/3212 20130101; C23F 3/06 20130101 |
Class at
Publication: |
438/689 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
1-38. (canceled)
39. A polishing method for removing at least a portion of a metal
film, comprising mechanically rubbing a metal film surface using a
chemical mechanical polishing formulation comprising an oxidizing
agent and a corrosion inhibitor said formulation having a pH in the
range of from about 0.1 to 6.9.
40. The polishing method according to claim 39, wherein the
oxidizing agent is an iodate salt.
41. The polishing method according to claim 39, wherein the
oxidizing agent is selected from the group consisting of hydrogen
peroxide, potassium iodate, ferric nitrate, ammonium chlorite,
ammonium chlorate, ammonium iodate, ammonium perborate, ammonium
perchlorate, ammonium periodate ammonium persulfate,
tetramethylammonium chlorite, tetramethylammonium chlorate,
tetramethylammonium iodate, tetramethylammonium perborate,
tetramethylammonium perchlorate, tetramethylammonium periodate,
tetramethylammonium persulfate, urea hydrogen peroxide,
4-methylmorpholine N-oxide (C.sub.5H.sub.11NO.sub.2) and pyridine
N-oxide (C.sub.5H.sub.5NO).
42. The polishing method according to claim 39, wherein the
corrosion inhibitor is a carboxylic acid.
43. The polishing method according to claim 39, wherein the
corrosion inhibitor is selected from the group consisting of
glycine, oxalic acid, malonic acid, succinic acid and
nitrilotriacetic acid.
44. The polishing method according to claim 39, wherein the
corrosion inhibitor is a dicarboxylic acid.
45. The polishing method according to claim 44, wherein the
dicarboxylic acid has a nitrogen containing functional group.
46. The polishing method according to claim 44, wherein the
dicarboxylic acid is iminodiacetic acid.
47. The polishing method according to claim 46, wherein the
dicarboxylic acid is iminodiacetic acid.
48. The polishing method according to claim 39, wherein the metal
film comprises copper, a copper alloy or a copper compound having
copper as its principal component.
49. The polishing method according to claim 39, wherein the metal
film comprises aluminum, an aluminum alloy or an aluminum compound
having aluminum as its principal component.
50. The polishing method according to claim 39, wherein the metal
film comprises tungsten, a tungsten alloy or a tungsten compound
having tungsten as its principal component.
51. The polishing method according to claim 50, wherein the
tungsten compound is a tungsten nitride., tantalum, tantalum
nitride, silicon doped tantalum nitride, titanium nitride and
silicon doped titanium nitride
52. The polishing method according to claim 39, wherein the metal
film is selected from the group consisting of titanium, a titanium
alloy, or a titanium compound having titanium as its principal
component.
53. The polishing method according to claim 52, wherein the
titanium compound is selected from the group consisting of titanium
nitride and silicon doped titanium nitride.
54. The polishing method according to claim 39, wherein the metal
film is selected tantalum, a tantalum alloy or a tantalum compound
having tantalum as its principal component.
55. The polishing method according to claim 54, wherein the
tantalum compound is selected from the group consisting of tantalum
nitride and silicon doped tantalum nitride.
56. The polishing method according to claim 39, wherein said
formulation, further comprises an activating agent.
57. The polishing method according to claim 56, wherein the
activating agent is selected from the group consisting of inorganic
and organic acids.
58. The polishing method according to claim 57, wherein the
inorganic acid is selected from the group consisting of phosphoric
acid, fluoroboric acid, and iodic acid.
59. The polishing method according to claim 57, wherein the organic
acid is selected from the group consisting of citric acid, malic
acid,
60. The polishing method according to claim 39, further comprising
a pH modifier in such amounts to modify the pH to a region of about
0.1 to 6.9, wherein said pH modifier is selected from the group
consisting of: potassium hydroxide, sodium hydroxide, ammonium
hydroxide, tetramethylammonium hydroxide, or quaternary ammonium
hydroxide.
61. The polishing method according to claim 39, wherein said
formulation further comprises a cleaning agent.
62. The polishing method according to claim 61, wherein the
cleaning agent is a carboxylic acid.
63. The polishing method according to claim 61, wherein the
cleaning agent is selected from the group consisting of glycine,
oxalic acid, malonic acid, succinic acid, citric acid and
nitrilotriacetic acid.
64. The polishing method according to claim 61, wherein the
cleaning agent is a dicarboxylic acid.
65. The polishing method according to claim 64, wherein the
dicarboxylic acid has a nitrogen containing functional group.
66. The polishing method according to claim 65, wherein the
dicarboxylic acid is iminodiacetic acid.
67. The polishing method according to claim 39, wherein said
formulation further comprises an activating agent and a cleaning
agent.
68. The polishing method according to claim 67, wherein said
formulation comprises:
4 a Oxidizer 0.1 to 20% by weight b. Corrosion inhibitor 0 to 5% by
weight c. Activating agent 0 to 5% by weight d. Cleaning agent 0 to
5% by weight
69. The polishing method according to claim 68, further comprising
a pH modifier in such amounts to modify the pH to a region of about
0.1 to 6.9, wherein said pH modifier is selected from the group
consisting of: potassium hydroxide, sodium hydroxide, ammonium
hydroxide, tetramethylammonium hydroxide, or quaternary ammonium
hydroxide.
70. The polishing method according to claim 68, wherein the
cleaning agent is an inorganic acid.
71. The polishing method according to claim 68, wherein the
corrosion inhibitor is iminodiacetic acid.
72. The polishing method according to claim 39, wherein the
formulation comprises:
5 a. HIO.sub.3 4% by weight b. IDA 0.2% by weight C.
H.sub.3PO.sub.4 0.75% by weight d. KOH 1.73% by weight e. Water
balance
73. The polishing method according to claim 72, wherein the pH of
the formulation is in the range of from about 0.1 to 6.9.
74. The abrasive free polishing formulation according to claim 72,
wherein the pH of the formulation is about 3.5.
75. The polishing method according to claim 68, wherein the
oxidizing agent is selected from the group consisting of: hydrogen
peroxide, potassium iodate, ferric nitrate, ammonium chlorite,
ammonium chlorate, ammonium iodate, ammonium perborate, ammonium
perchlorate, ammonium periodate ammonium persulfate,
tetramethylammonium chlorite, tetramethylammonium chlorate,
tetramethylammonium iodate, tetramethylammonium perborate,
tetramethylammonium perchlorate, tetramethylammonium periodate,
tetramethylammonium persulfate, urea hydrogen peroxide,
4-methylmorpholine N-oxide (C.sub.5H.sub.11NO.sub.2) and pyridine
N-oxide (C.sub.5H.sub.5NO).
Description
[0001] This application is a divisional of U.S. application Ser.
No. 09/9535,805, filed on Aug. 23, 2001, now allowed.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates generally to the chemical
mechanical polishing of semiconductor devices systems and methods,
and more particularly, to a formulation and method for use in
polishing metal films in semiconductor interconnection
processes.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to a polishing formulation for
surfaces of a semiconductor wafer, and more particularly, to a
polishing formulation and a method for using the polishing
formulation to remove and polish metal containing materials layered
on semiconductor wafer surfaces.
[0004] Semiconductor wafers are used to form integrated circuits.
The semiconductor wafer typically includes a substrate, such as
silicon, upon which dielectric materials, barrier materials, and
metal conductors and interconnects are layered. These different
materials have insulating, conductive or semi-conductive
properties. Integrated circuits are formed by patterning regions
into the substrate and depositing thereon multiple layers of
dielectric material, barrier material, and metals.
[0005] In order to meet the higher speeds required in large scale
integration (LSI), semiconductor manufacturers are looking to
copper and its alloys for interconnections due to its decreased
resistivity. Copper is also less vulnerable to electromigration
than aluminum and less likely to fracture under stress.
[0006] In conventional deposition, a layer of metal and a layer of
a masking material called photoresist are deposited on a silicon
wafer. Unwanted metal is then etched away with an appropriate
chemical, leaving the desired pattern of wires or vias. Next, the
spaces between the wires or vias are filled with silicon dioxide or
other low k dielectric as insulator, and finally the entire wafer
surface is polished to provide a planar surface and/or remove
excess insulator. In copper deposition the damascene method is used
wherein the pattern of wires or vias is first formed by etching the
silicon dioxide or other suitable insulator such as fluorinated
silica glass, Silk.RTM.), or methylsilsesquioxane etc. The metal is
then deposited second.
[0007] Typically for copper technology, the layers that are removed
and polished consist of a copper layer (about 1-1.5 .mu.m thick) on
top of a thin copper seed layer (about 0.05-0.15 .mu.m thick).
These copper layers are separated from the dielectric material
surface by a layer of barrier material (about 50-300 .ANG.
thick).
[0008] In order to obtain the correct patterning, excess material
used to form the layers on the substrate must be removed. Further,
to obtain efficient circuits, it is important to have a flat or
planar semiconductor wafer surface. Thus, it is necessary to polish
certain surfaces of a semiconductor wafer.
[0009] Chemical Mechanical Polishing or Planarization ("CMP") is a
process in which material is removed from a surface of a
semiconductor wafer, and the surface is polished (planarized) by
coupling a physical process such as abrasion with a chemical
process such as oxidation or chelation. In its most rudimentary
form, CMP involves applying slurry, a solution of an abrasive and
an active chemistry, to a polishing pad that buffs the surface of a
semiconductor wafer to achieve the removal, planarization, and
polishing process.
[0010] Copper CMP often employs a two-step slurry approach. The
slurry used in the first step has a high copper removal rate and a
comparatively low barrier material removal rate. The slurry used in
the second step has a relatively high barrier material removal
rate, comparable removal rate for copper and low or comparable
removal rate on the dielectric material.
[0011] As successive layers are deposited across previously
patterned layers of an integrated circuit, elevational disparity
develops across the surface of each layer. If left unattended, the
elevational disparities in each level of an integrated circuit can
lead to various problems. For example, when dielectric, conductive,
or semiconductive material is deposited over a topological surface
having elevationally raised and recessed regions, step coverage
problems may arise. Step coverage is defined as a measure of how
well a film conforms over an underlying step and is expressed by
the ratio of the minimum thickness of a film as it crosses a step
to the nominal thickness of the film over horizontal regions. Also,
stringers or fences may arise from incomplete etching, polishing,
or redeposition of metal.
[0012] One key to obtaining good uniformity across the wafer
surface is by using a polishing formulation that has a higher
removal selectivity for copper than the underlying barrier layer.
If such selectivity is not maintained, unwanted dishing of copper
and/or erosion of the dielectric material may occur.
[0013] Typical commercial CMP slurries used to remove overfill
material and polish semiconductor wafer surfaces have a barrier
material removal rate below 500 .ANG./min. Further, these slurries
have a copper to barrier material removal rate selectivity of
greater than 4:1. This disparity in removal rates during the
removal and polishing of the barrier material results in
significant dishing of copper on the surface of the semiconductor
wafer and/or poor removal of the barrier material.
[0014] Another problem with conventional CMP slurries is that the
removal chemistry of the slurry is compositionally unstable. CMP
slurries using ceria, alumina, or fumed silica must be continuously
agitated or the abrasive particles will rapidly settle out.
Further, many of the colloidal and fumed abrasives agglomerate
after relatively short time frames following addition to the
supporting chemistry. Both of these problems lead to significant
operational obstacles such as the need for an expensive
continuously recirculating distribution system equipped with
filtration, chemistry monitoring, chemical addition equipment, and
on-line particle monitors.
[0015] A further problem in commercial CMP slurries is that the
abrasive materials in the slurries produce defects in the form of
micro scratches. The scratches and other defects occur due to the
solid abrasive, in particular alumina, which is the main material
used as a metal polishing abrasive. Slurry remains behind in the
micro-scratches causing the semiconductor device to fail. Micro
scratches and poor planarization efficiency result in integrated
circuits with increased defects and a lower yield.
[0016] Further, abrasive particles remain behind on the substrate
surface after CMP. Cleaning machines or scrubbers using mechanical
cleaning must be employed to remove the excess material.
[0017] Still another problem of commercial CMP slurries is that the
chemicals that make up the slurries produce a copper surface that
has a high corrosion tendency post polish.
[0018] A further problem that occurs in commercial CMP relates to
the peeling of the metal film surface from the substrate due to
frictional force between the polishing abrasive and the metal film
surface.
[0019] A still further problem that exists for semiconductor
manufacturers in commercial CMP is the cost of abrasives, polishing
pads, slurry feeders, processor for slurry containing waste and
stirrers to prevent sedimentation of the abrasive in the slurry
feeder.
[0020] Further, since CMP machines are set up in cleanroom
environments, the dust generated by the solid abrasive material
must be kept to a minimum This requires expensive systems to be
installed to suppress dust in the exhaust duct of the CMP
machine;
[0021] Therefore, it is an object of this invention, to provide an
abrasive free polishing formulation for the removal of copper and
other metal interconnects that overcomes the current problems in
CMP processing.
[0022] An object of this invention, therefore, is to provide an
abrasive free polishing formulation having a high copper removal
rate; high uniformity of the planarized surface and a comparatively
low barrier material removal rate with minimal dishing and/or
erosion.
[0023] These and other objects and advantages of the invention will
be apparent to those skilled in the art upon reading the following
detailed description and upon reference to the drawings.
SUMMARY OF THE INVENTION
[0024] The present invention relates to an abrasive free polishing
formulation for removing at least a portion of a metal film
deposited during a semiconductor-processing step. The present
invention eliminates or reduces disadvantages associated with
chemical mechanical polishing processes comprising abrasive
components and provides an important technical advantage by
eliminating the abrasive component of the slurry thereby reducing
the cost of ownership to semiconductor manufacturing
facilities.
[0025] The present invention is directed to an abrasive-free
polishing formulation, which has a high removal rate on copper and
a low removal rate on barrier material and a method of polishing a
metal containing material using the abrasive free polishing
formulation.
[0026] The present invention is directed to a non-abrasive
polishing formulation comprising a first slurry, which has a high
removal rate on copper and a low removal rate on barrier material
and a chemical mechanical polishing method of using the
non-abrasive polishing formulation.
[0027] More specifically, in one aspect, the present invention
relates to an abrasive free polishing formulation for removing at
least a portion of a metal film, comprising an oxidizing agent and
a corrosion inhibitor said formulation having a pH in the range of
from about 0.1 to 6.9.
[0028] In a further aspect, the present invention relates to a
polishing method for removing at least a portion of a metal film,
comprising mechanically rubbing a metal film surface using a
solution comprising an oxidizing agent and a corrosion inhibitor
said formulation having a pH in the range of from about 0.1 to
6.9.
[0029] As will become apparent from the discussion that follows,
the stable abrasive free formulation and method of using said
formulation provide for removal of material and polishing of
semiconductor wafer surfaces with significantly no dishing or oxide
erosion, with significantly no surface defects and good
planarization efficiency, and produce a copper surface with minimal
corrosion tendency post-polish.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a cross sectional view of a semiconductor wafer
prior to chemical mechanical polishing with the abrasive free
formulation of the present invention.
[0031] FIG. 2 is a cross sectional view of the semiconductor wafer
of FIG. 1 following chemical mechanical polishing with the abrasive
free formulation of the present invention.
[0032] FIG. 3 is a cross sectional view of a semiconductor wafer
illustrating copper dishing.
[0033] FIG. 4 is a cross sectional view of a semiconductor wafer
illustrating oxide or dielectric erosion.
[0034] FIG. 5 is a plot showing planarization performance and step
height reduction at room temperature of one abrasive free slurry
formulation of the present invention.
[0035] FIG. 6 is a plot showing planarization performance and array
recess at room temperature of one abrasive free slurry formulation
of the present invention.
[0036] FIG. 7 is a plot showing planarization performance and step
height reduction at 45.degree. C. of one abrasive free slurry
formulation of the present invention.
[0037] FIG. 8 is a plot showing planarization performance and array
recess at 45.degree. C. of one abrasive free slurry formulation of
the present invention.
[0038] FIG. 9 is a plot showing planarization performance and step
height reduction at room temperature of a second abrasive free
formulation of the present invention.
[0039] FIG. 10 is a plot showing planarization performance and
array recess at room temperature of a second abrasive free slurry
formulation of the present invention.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
THEREOF
[0040] The disclosure of the following United States patent
application, which is commonly owned by assignee of the present
application is hereby incorporated herein by reference in its
entirety:
[0041] U.S. patent application Ser. No. 09/562,298 filed on May 1,
2000 in the names of Thomas H. Baum, et al.
[0042] The present invention provides an abrasive free chemical
mechanical polishing formulation and method of using such
formulation for removing and polishing the bulk copper layer of a
damascene processing step in the manufacturing of an integrated
circuit.
[0043] Applicants' co pending U.S. patent application Ser. No.
09/562,298 discloses a first and second slurry wherein the first
slurry is used to remove bulk copper down to a barrier layer. The
first slurry has a high removal rate on copper and a low removal
rate on barrier material and comprises silica particles, an
oxidizing agent, a corrosion inhibitor, and a cleaning agent. More
particularly the first slurry is preferentially comprised of 1-10%
colloidal silica with particle size range of from 3 to 100 nm, or
1-5% fumed silica with mean particle size of less than about 700
nm, about 1-12% potassium iodate (KIO.sub.3, formed by reaction of
HIO.sub.3 with KOH), which is used as the oxidizing agent for the
copper, about 0-5% concentrated inorganic acid as a copper
activating agent, and 0-2% iminodiacetic acid (IDA) as the copper
corrosion inhibitor and cleaning agent.
[0044] In an effort to solve the aforementioned problems relating
to the abrasive portion of the CMP slurry, which are summarized
below:
[0045] reduction of scratches caused by the solid abrasive;
[0046] peeling due to frictional force between the polishing
abrasive and the metal film surface during CMP;
[0047] mechanical cleaning step to remove polishing abrasive left
behind after the polishing step;
[0048] cost of abrasives, polishing pads, slurry feeders, processor
for slurry containing waste and pumps, filters, monitoring
equipment, and stirrers to prevent sedimentation of the abrasive in
the slurry distribution system; and
[0049] a system to suppress dust in the exhaust duct of the CMP
machine, the inventors of the present invention experimentally
removed the abrasive component of the CMP slurry, and used the
abrasive free formulation to chemical mechanically polish a wafer
having deposited thereon a bulk copper layer from a damascene
processing step. The inventors unexpectedly discovered that the
particular combination of potassium iodate, inorganic acid, and
iminodiacetic acid removed the bulk copper layer at a rate >3100
.ANG./min and as high as 4000 .ANG./min in preliminary testing.
Such removal rates are not significantly different from the same
formulation comprising abrasive.
[0050] The present invention presents a novel abrasive free
chemical mechanical polishing formulation that overcomes the
deficiencies in the prior art while providing a manufacturable
process that may be implemented in the semiconductor-manufacturing
arena with little or no alterations to the current CMP systems and
footprints. As will become apparent from the examples that follow,
the stable abrasive free CMP formulation and method of using such
formulation of the present invention provide for removal of
material and polishing of semiconductor wafer surfaces with
significantly no dishing or oxide erosion, with significantly no
surface defects and good planarization efficiency.
[0051] Table 1, below outlines a comparison between the first
slurry formulation of U.S. patent application Ser. No. 09/562,298
and one formulation of the abrasive free first slurry of the
present invention. Both formulations comprise about 1-12% potassium
iodate (KIO.sub.3, formed by reaction of HIO.sub.3 with KOH), which
is used as the oxidizing agent for the copper, about 0-5%
concentrated inorganic acid as a copper activating agent, and 0-2%
iminodiacetic acid (IDA) as a copper corrosion inhibitor and
cleaning agent. Additionally, the First Slurry of U.S. patent
application Ser. No. 09/562,298 further comprises either
precipitated spherical silica particles in the size range of 3 to
100 nm, or fumed silica with mean particle size less than about 700
nm.
1TABLE 1 Comparison of Removal Rates of First Slurries on Different
Materials based on the preferred embodiment of U.S. Patent
Application No. 09/562,298 as compared to the abrasive free
polishing formulation (AFS) of the present invention. First Slurry
Selectivity First Slurry Selectivity Removal Rates* Material:Cu
Removal Rates** Material:Cu (.ANG./min) First Slurry (.ANG./min)
First Slurry LAYER (U.S. Pat. No. 09/562,298) (U.S. Pat. No.
09/562,298) (AFS) (AFS) Copper >5000 >3500 Tantalum <500
1:10 <8 1:500 Tantalum <500 1:10 <60 1:61 Nitride Thermal
Oxide <150 1:50 <5 1:730 *(Down Force = 5 psi, Flow Rate =
200 mL/min, Table Speed = 90 rpm, Quill Speed = 50 rpm, Pad Type =
IC 1000) **(Down Force = 4 psi, Flow Rate = 160 mL/min, Table Speed
= 125 rpm, Quill Speed = 116 rpm, Pad Type = IC 1000)
[0052] In one embodiment, the present invention is directed to an
aqueous abrasive free polishing formulation comprising an oxidizing
agent and a copper corrosion inhibitor agent having a pH in a range
of from about 0.1 to 6.9. More preferably the pH of the formulation
is in the range from about 2 to 5 and most preferably, the pH of
the polishing formulation is in the range of from about 3 to 4.
[0053] In a further embodiment, the present invention is directed
to an aqueous abrasive free polishing formulation comprising 0.1 to
20 weight percent oxidizing agent and 0 to 5 weight percent copper
corrosion inhibitor agent and 0-5 weight percent activating agent,
said formulation having a pH in a range of from about 0.1 to 6.9.
More preferably the pH of the formulation is in the range from
about 2 to 5 and most preferably, the pH of the polishing
formulation is in the range of from about 3 to 4.
[0054] As used herein, the term oxidizing agent is defined as any
substance which removes metal electrons and raises the atomic
valence and includes but is not limited to hydrogen peroxide
(H.sub.2O.sub.2), ferric nitrate (Fe(NO.sub.3).sub.3) and potassium
iodate (KIO.sub.3), nitric acid (HNO.sub.3), ammonium chlorite
(NH.sub.4CIO.sub.2), ammonium chlorate (NH.sub.4CIO.sub.3),
ammonium iodate (NH.sub.4IO.sub.3), ammonium perborate
(NH.sub.4BO.sub.3), ammonium perchlorate (NH.sub.4CIO.sub.4),
ammonium periodate (NH.sub.4IO.sub.3), ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8), tetramethylammonium chlorite
((N(CH.sub.3).sub.4)CIO.sub.2), tetramethylammonium chlorate
((N(CH.sub.3).sub.4)CIO.sub.3), tetramethylammonium iodate
((N(CH.sub.3).sub.4)IO.sub.3), tetramethylammonium perborate
((N(CH.sub.3).sub.4)BO.sub.3), tetramethylammonium perchlorate
((N(CH.sub.3).sub.4)CIO.sub.4), tetramethylammonium periodate
((N(CH.sub.3).sub.4)IO.sub.4), tetramethylammonium persulfate
((N(CH.sub.3).sub.4)S.sub.2O.sub.8), urea hydrogen peroxide
((CO(NH.sub.2).sub.2)H.sub.2O.sub.2). The preferred oxidizing agent
for the abrasive free formulation of the instant invention is
potassium iodate formed by reaction of HIO.sub.3 with KOH.
Preferably, the oxidizing agent of the present invention is
potassium iodate.
[0055] Alternatively, the oxidizing agent may comprise an amine
N-oxide having the formula (R.sub.1R.sub.2R.sub.3N.fwdarw.O),
wherein R.sub.1R.sub.2R.sub.3 are independently selected from the
group consisting of: H and C.sub.1-C.sub.8 alkyl. Specific examples
of amine N-oxides include but are not limited to 4-methylmorpholine
N-oxide (C.sub.5H.sub.11NO.sub.2) and pyridine N-oxide
(C.sub.5H.sub.5NO).
[0056] Further, as used herein, the term copper-activating agent is
defined as any substance that in the presence of a water containing
solution solubilizes or etches the oxidized copper material. Copper
activating agents useful in the present invention include but are
not limited to mineral acids (i.e. hydrochloric acid, nitric acid),
inorganic acids (i.e. phosphoric acid, fluoroboric acid) and
organic acids (i.e. oxalic acid, malonic acid, malic acid, citric
acid, acetic acid and pivalic acid).
[0057] In a further embodiment, the abrasive free CMP formulation
of the present invention, may comprise, an oxidizing agent, an
activating agent, a corrosion inhibitor and optionally a cleaning
agent. The chemistry of the formulation should be stable and have a
pH in the range of about 0.1 to 6.9 and more preferably between
about 2 to 5. More preferably, the abrasive free polishing
formulation comprises from about 1-13% potassium iodate (KIO.sub.3,
formed by reaction of HIO.sub.3 with KOH), which is used as the
oxidizing agent for the copper, about 0-5% concentrated inorganic
acid as the copper activating agent, and 0-2% iminodiacetic acid
(IDA) as the copper corrosion inhibitor agent.
[0058] The formulation may further comprise potassium hydroxide,
tetramethylammonium hydroxide (or related quaternary ammonium
hydroxide) or ammonium hydroxide in such amounts as to adjust the
pH to the desired level. A buffering solution of suitable identity
could also be used to adjust the pH value.
[0059] As used herein the copper corrosion inhibitor is defined as
a substance that reacts with the oxidized copper thin film to
passivate the copper layer and prevent excessive etching of the
copper surface during CMP and the cleaning agent is defined as a
substance that chelates to the copper, leading to soluble copper
complexes that can be readily removed during polishing. The
corrosion inhibitor and cleaning agent for the abrasive free
formulation are preferably a carboxylic acid. More specifically,
the carboxylic acid may be chosen from, but not limited to glycine,
oxalic acid, malonic acid, succinic acid, citric acid, and
nitrilotriacetic acid. Alternatively, the carboxylic acid may be a
dicarboxylic acid that preferentially has a nitrogen containing
functional group. In the most preferred form, the corrosion
inhibitor and the cleaning agent are iminodiacetic acid.
[0060] Referring to FIG. 1, the present invention includes a method
for chemical mechanical polishing of a copper containing material
14, preferably a copper containing material from a damascene
processing step, comprising the following steps: (1) providing an
abrasive free first chemical mechanical polishing slurry that has a
high removal rate on copper 14 and a low removal rate on barrier
material 13; (2) chemical mechanically polishing a semiconductor
wafer surface 10 with the abrasive free slurry, wherein the
abrasive free chemical mechanical polishing formulation comprises
an oxidizing agent and an activating agent and said formulation
having a pH in a range from about 0.1 to 6.9.
[0061] The method of the present invention, overcomes the problems
associated with the abrasive component of the first slurry chemical
mechanical processing step in that:
[0062] scratches caused by the solid abrasive are eliminated;
[0063] peeling due to frictional force between the polishing
abrasive and the metal film surface during CMP are eliminated;
[0064] mechanical cleaning step to remove polishing abrasive left
behind after the polishing step is eliminated;
[0065] cost of abrasives, polishing pads, slurry feeders, processor
for slurry containing waste and pumps, filters, monitoring
equipment, and stirrers to prevent sedimentation of the abrasive in
the slurry distribution system are reduced or eliminated; and
[0066] a system to suppress dust in the exhaust duct of the CMP
machine is eliminated.
[0067] Generally, the slurry is applied to a pad contained on a
polishing instrument. Polishing instrument parameters such as down
force (DF), flow rate (FR), table speed (TS), quill speed (QS), and
pad type can be adjusted to effect the results of the CMP slurry.
These parameters are important in obtaining efficient planarization
results and limiting dishing and erosion. Although these parameters
may be altered, when used with the CMP slurry of the present
invention, the standard conditions used are DF in a range of from
about 3-6 psi, FR in a range of from about 100-200 mL/min, TS in a
range of from about 80 to 150 rpm, QS in a range of from about 50
to 130 rpm, and the IC 1000 pad type. Preferably the conditions
used in the present invention include DF of 4 psi, FR of 160
mL/min, TS of 125 rpm, QS of 116 rpm, and the Rodel IC 1000 pad
type.
[0068] FIG. 2 illustrates the semiconductor wafer 10 of FIG. 1,
after steps (1) and (2) of the present method for CMP have been
carried out, and the semiconductor wafer surface has been polished
with the abrasive free chemical mechanical polishing formulation of
the present invention. When FIG. 2 is compared to FIG. 1, the top
copper layer 14 in FIG. 1 has been preferentially removed, and only
the copper in the trenches (FIG. 2) 18a, 18b, and 18c is left. As
shown in FIG. 2 the barrier material layer 17 is substantially
intact, and the dielectric material 16 based on substrate 15 is
still unexposed.
[0069] By using the abrasive free polishing formulation of the
present invention, with the selectivities described in Table 1, and
following the described method, copper dishing (FIG. 3) and oxide
erosion (FIG. 4) can be reduced. FIG. 3 shows a semiconductor wafer
to which a CMP slurry has been applied, which had a higher
selectivity for copper 26a, 26b, 26c than for the barrier material
25a, 25b, 25c or dielectric material 24. As a result, disparate
amounts of copper are removed from the surface of the semiconductor
wafer. This is known as copper dishing and is shown by the
dish-like troughs 27a, 27b, and 27c in the trenches of copper 26a,
26b, 26c. The abrasive free CMP formulation of the present
invention and method of using this formulation greatly reduces
copper dishing.
[0070] FIG. 4 shows a semiconductor wafer to which a CMP slurry has
been applied, which has a higher selectivity for the dielectric
material 29 than for the barrier material 30a, 30b, 30c, or copper
31a, 31b, 31c. As a result, disparate amounts of dielectric
material are removed from the surface of the semiconductor wafer.
This is known as oxide erosion or dielectric erosion and is shown
by the indentions and/or reduction of the dielectric material 29a,
29b. The abrasive free CMP formulation of the present invention and
method of using such formulation greatly reduces oxide erosion or
dielectric erosion.
[0071] During the damascene process, grooves are dry etched into an
insulating thin film to form an interconnect pattern. Copper or
copper alloy is deposited over the entire wafer surface, reflecting
the groove which is the interconnect pattern. If left unattended,
the elevational disparities in each level of an integrated circuit
can lead to various problems. For example, when dielectric,
conductive, or semiconductive material is deposited over a
topological surface having elevationally raised and recessed
regions, step coverage problems may arise. Step coverage is defined
as a measure of how well a film conforms over an underlying step
and is expressed by the ratio of the minimum thickness of a film as
it crosses a step to the nominal thickness of the film over
horizontal regions. Also, stringers may arise from incomplete
etching, polishing, or redeposition of metal.
[0072] The present invention provides a method for planarizing and
polishing at least a portion of a surface of a semiconductor wafer
onto which has been deposited a metal containing layer. The method
comprising the steps of:
[0073] providing an aqueous polishing formulation comprising an
oxidizing agent, and an activating agent, said polishing
formulation having a pH in a range of from about 0.1 to 6.9;
and
[0074] chemical mechanically polishing a semiconductor wafer
surface with said formulation.
[0075] The formulation of the present invention oxidizes the copper
metal layer, to form a thin metal oxide layer on the substrate
surface. The activating agent solubilizes and/or etches the thin
oxide layer and under CMP conditions, the removal of the thin oxide
layer is accelerated by the friction imposed on the oxide layer by
the polishing pad. Because the pad, contacts only the projections
on the wafer surface, the polishing occurs more slowly in the lower
level topography regions, resulting in a wafer surface having
improved planarization.
[0076] Although the present invention is directed to removal of
copper and copper containing materials, it is not this limited to
such. The present invention is also useful for polishing and
planarizing other materials useful as interconnects in
semiconductor related applications including but not limited to
aluminum, aluminum alloys, aluminum compounds having aluminum as
its principal component, tungsten, tungsten alloys, tungsten
compounds having tungsten as its principal component, (i.e.,
tungsten nitride), tantalum, tantalum nitride, silicon doped
tantalum nitride, titanium, titanium alloys and titanium compounds
having titanium as its principal component (i.e., titanium nitride
and silicon doped titanium nitride).
[0077] The copper containing material removed in the present
invention may be deposited in any number of ways and as such is not
limited to the examples provided herein. Specific methods for
depositing copper containing thin films include CVD, PVD,
electroplating, and electroless deposition.
[0078] The formulation of the present invention is useful for
removal and planarization of the bulk copper layer deposited in a
damascene process step, but is not limited to such. The present
invention may be useful for removing copper and copper containing
materials from any substrate comprising same.
[0079] Further, the abrasive free formulation of the present
invention may be useful in processes relating to: cleaning
semiconductor wafer surfaces; bulk metal removal; planarization;
first step underpolishing; first step overpolishing, and neutral or
intermediate first step polishing.
[0080] Further, the present invention may further comprise a second
polishing step comprising a formulation having a high removal rate
on barrier material a low or comparable removal rate on copper and
a low removal rate on the dielectric material.
[0081] The features, aspects and advantages of the present
invention are further shown with reference to the following
non-limiting examples relating to the invention.
EXAMPLES
Example 1
Polishing Performance Comparison of Abrasive Free Slurry
Formulations (AFS) 1 and 2.
[0082] Table 2 provides a summary of the composition of two
abrasive free slurries for polish performance comparison and Table
3 provides actual experimental results for the abrasive free
polishing formulation as used on 8" blanket films wafers of the
following composition and thickness: copper wafer (5,000 .ANG.
thermal oxide, 300 .ANG. tantalum, 1,500 .ANG. PVD copper seed
layer and 15,000 .ANG. electroplated copper), tantalum nitride
wafer (5,000 .ANG. thermal oxide and 3,000 .ANG. tantalum nitride),
tantalum wafer (5,000 .ANG. thermal oxide and 3,000 .ANG.
tantalum), and plasma enhanced tetraethyl orthosilicate (9,000
.ANG. PETEOS).
2TABLE 2 Abrasive Free Slurry (AFS) Formulations AFS 1 and AFS 2
AFS 1 Final Weight AFS 2 Final Weight Component Percent Component
Percent HIO.sub.3 4.00 HIO.sub.3 4.00 IDA 0.20 IDA 0.20
H.sub.3PO.sub.4 0.75 Citric Acid 0.20 KOH 1.73 KOH 1.37 H.sub.2O
Balance H.sub.2O balance
[0083]
3TABLE 3 Polishing Performance Comparison AFS 1 vs. AFS 2 AFS 1**
AFS 2 Room Temp. 45.degree. C. Room Temp. 45.degree. C. Cu RR*
(.ANG./min) 3166 3421 3513 3926 TaN RR (.ANG./min) 34.76 1 (neg)*
57.65 N/A Ta RR (.ANG./min) 0.6383 1 (neg)* 7.03 N/A PETEOS
(.ANG./min) 4.85 24 4.81 N/A Selec. Cu:TaN 91.11 3400 600 N/A
Selec. Cu:Ta 4960 3400 61 N/A Selec: Cu:PETEOS 653 1425 730 N/A *RR
represents removal rate **For AFS 1 & 2 (Down Force = 4 psi,
Flow Rate = 160 mL/min, Table Speed = 125 rpm, Quill Speed = 116
rpm, Pad Type = IC 1000)
Example 2
Planarization Performance and Step Height Reduction
[0084] One object of CMP processing is to produce a uniform surface
on the semiconductor wafer. The uniformity of the planarized
surface is a function of several factors. FIGS. 5 and 7 are plots
showing the step height remaining verses different
copper/dielectric pattern densities on a Sematech 854 CMP AZ mask
test wafer after underpolishing with an abrasive free polishing
formulation for a bulk copper-polishing step according to one
embodiment of the present invention. The initial step height before
polishing was approximately 6000 .ANG.. The data plotted in FIG. 5
is based on room temperature experimental conditions and the data
plotted in FIG. 7, 45.degree. C. The substantial step height
reduction on the patterned wafers while underpolishing evidences
the commercial viability of the present invention.
Example 3
Planarization Performance and Array Recess
[0085] FIGS. 6 and 8 are plots showing the array recess verses
different copper/dielectric pattern densities based on using the
same abrasive free polishing formulation and substrate as in the
previous step height reduction experimental. The data plotted in
FIG. 6 is based on room temperature experimental conditions and the
data plotted in FIG. 8, 45.degree. C. The low levels of array
recess are further evidence of the commercial viability of the
abrasive free polishing formulation.
* * * * *